The present invention generally relates to a measuring instrument and more particularly, to an optical measuring head which employs optical fibers.
Conventionally, there has been employed an optical measuring head employing optical fibers for examination, for example, of a blood specimen 8 as shown in FIG. 4 or 7.
The known optical measuring head shown in FIG. 4 includes light projecting fibers 2 axially disposed side by side in a cable, and a light receiving fiber 4 also axially provided within the same cable as illustrated, and is so arranged that reflection of light projected onto the blood specimen 8 which is an object to be measured, from the light projecting fibers 2 is received by the light receiving fiber 4 so as to be transmitted to a measuring device (not shown) for measuring the nature or characteristics of the blood specimen 8 by the amount of the reflected light.
The known optical measuring head as described above, however, has such a problem that it is difficult to effect an accurate examination, since the amount of the reflected light tends to vary upon variation of the distance between said measuring head and the blood specimen 8.
There is also a similar problem in the case where the blood specimen 8 is composed of a transparent protective layer 9, a reacting layer (colored layer) 10, a white reflecting layer 11 and a developing layer 12 disposed one upon another from the side of the measuring head as shown in FIG. 6, and is so arranged that light by the light projecting fibers 2 is led from the transparent protective layer 9 to the reacting layer 10, while the light which has passed through the reacting layer 10 (i.e., the light except for that absorbed by the reacting layer 10) is reflected by the white reflecting layer 11 so as to be incident upon the light receiving fiber 4 through said reacting layer 10 and transparent protective layer 9, whereby the amount of the incident light (indicated by an arrow A in FIG. 6) is to be measured.
More specifically, in the above arrangement of FIG. 6, since light reflected by the transparent protective layer 9 and indicated by an arrow B also enters the light receiving fiber 4, besides the reflected light as indicated by the arrow A referred to above, there is such a disadvantage that an error takes place in the amount of light which has passed through the reacting layer 10 to represent the characteristics of the blood specimen 8, i.e., in the measurement of absorbance of light in the reacting layer 10.
Meanwhile, another conventional optical measuring head shown in FIG. 7 includes the light projecting fibers 2 and light receiving fiber 4 provided in the similar manner as in the measuring head of FIG. 4, and a convex lens 13 disposed in front of the light receiving fiber 4 so as to receive the reflected light from the blood specimen 8 in a converged state, and further, a casing 15 having a transparent glass plate 14 at its forward end and applied over the outer periphery of the head as indicated by two-dotted chain lines depending on necessity.
In the above optical measuring head in FIG. 7 also, there is involved the problem that the result of measurement is affected by the distance between the blood specimen 8 and the measuring head, while the reflected light from the glass 14 besides that by the transparent protective layer 9 enter the light receiving fiber 4 in the similar manner, thus making it difficult to effect an accurate measurement.